NMU: Revert problematic multiarch change to fix unusable -dev package (#909778)
libsdl2 (2.0.8+dfsg1-3.1) unstable; urgency=medium
.
* Non-maintainer upload.
* d/tests/build: Add autopkgtest to check that dynamic linking with
either pkg-config or sdl2-config works correctly
* Revert "Make libsdl2-dev coinstallable again"
(Closes: #909778) (reopens: #909740)